Sparking plug.



I. c. ORSWELL. SPARKING PLUG.

APPLICATION FILED APR-26. 1907.

1,1 64,1 13. Patented Dec. 14, 1915.

UNITED STATES PATENT oEEioE.

ISRAEL C. OBSWELL, OF HYDE PARK, MASSACHUSETTS, ASSIGNOR TO ORSWELLIGNI'IER COMPANY,.OF BOSTON, MASSACHUSETTS, A CORPORATION OF MAINE.

' SPABKING PLUG.

Application filed April 26, 1907.

To all whom it may concern:

Be it known that I, ISRAEL C. ORSWELL, a citizen of the United States,residing at Hyde Park, in the county of Norfolk and State ofMassachusetts, have invented an Improvement in Sparking Plugs, of whichthe following description, in connection with the accompanying drawings,is a specification, like letters on the drawings representing likeparts.

My invention relates to sparking devices for internal combustionengines, more particularly to the construction of sparking plugs andinduction coils therefor.

My invention aims generally to improve devices of this type by providingsimple and effective means for increasing the capacity and efficiency ofthe coil and perfecting the insulation thereof and to that end comprisesnovel features of construction and arrangement that will be bestunderstood and appre ciated by reference to the following descrip' tionwhen taken in connection with the accompanying drawings, of a spark plugembodying one form of my invention and selected for purposes ofillustration, its scope being more particularly pointed out in theappended claims.

In the drawings; Figure 1, is a vertical and longitudinal section takenthrough the axis of a spark plug, embodying a preferred form of myinvention, selected for illustration herein. Fig. 2, a perspective viewillus trating the manner of winding the induction coil. and insulatingthe secondary terminals thereof; Fig. 3, a similar View of the primarycoil to show the manner of carrying in one of the terminals of thesecondary and the manner of winding the latter; Fig. 4, a detailillustrating the method of winding and insulating the conductingconvolutions of the coils from one another; Fig. 5, a perspective detailof the insulation tabs or strips, to show the method of applying thesame to the secondary terminal; and Fig. 6, a perspective detailillustrating the porcelain disk through which the secondary terminalsare led to the sparking devices.

Referring to the drawings and to the particular embodiment of myinvention selected for illustration therein, I show a sparking plug thatis particularly, though not exclusively, adapted for use with internalcombnstion engines for automobiles, launches, and the like.

l Specification of Letters Patent.

Patented Dec. 14., 1915.

Serial No. 370,347.

This plug comprises a casing to receive an induction coil and suitablesparking electrodes, uniting in a single and compact structure theessential parts of a sparking device. In the present instance, referringtoFig. 1, the induction coil comprises primary and secondary windingsefficiently insulated from one another and the metallic conductingportions of the casing. The coil is provided with a core 1, preferablyformed of a bundle of soft iron wires, inclosed in a shell or sleeve 2of suitable insulating material, which, as herein, is preferablysomewhat longer than the core, so as to insulate the ends of the latterfrom the windings of the coil. This core receives the primary winding 3,shown in section in Fig. l, which is suitably wound thereon andcomprises, in the present instance, a plurality, herein two, layers ofwire having the terminals 4, Fig. 1, led up through the top of a casing5, with which the spark plug is provided, to suitable binding posts 6mounted upon its outer end (the top, Fig. 1). Each of the layers of theprimary winding and also those of the secondary, presently described,comprise a number of convolutions or strands 7, Figs. 3 and 4 of bare oruninsulated wire and intervening convolutions or strands, 8, of silk orother suitable insulating material, said strands being wound together,side by side around the core or upon an inner layer. By this arrangementthe silk strands, which intervene between the adjacent conductingconvolutions of bare or naked wire, forfn the only insulating mediumbetween them. The successive layers of the windings of-the coilsare'insulated from one another by suitable insulating material, 9,herein preferably sheets of varnished fabric, paper, oil silk, or thelike, which are of high insulating properties. Outside of the primarywinding, 3, is a layer or shell, 10, of insulating material, upon whichthe secondary coil is wound, said shell being similar to the sheets 9,described, but preferably thicker effectually to insulate the primaryand secondary windings from one another.

The secondary coil or winding, Figs. 1 and 2, comprises a plurality oflayers of the relatively fine bare wire, 7, with the intermediateinsulating strands 8 and the insulating sheets 9, described. The windingof this coil and the manner of carrying out and insulating its leadwires or terminals ll, 12, is a feature of considerable impor tance. Ashere shown, suitable tabs or strips 13, 14 of insulating material arelaid lengthwise upon said terminals to insulate them from the bare orinsulated wires of the sec-- ondary and from one another. While it is amatter of individual preference whether both of these terminals bedirectly connected to the sparking electrodes or .one of them groundedupon the casing which is in electrical connection with one of theelectrodes, l have found the most advantageous results to be secured andprovide a more eiiicient strip having a perforation or aperture at itsfolded end to permit said terminal 11 to be led therethrough to centerthe same within its insulating envelop.

The terminal, thus insulated, is. laid longitudinally or lengthwise uponthe insulating shell of the primary coil, Fig; 3, and the winding iscommenced at about one fourth of an inch from the end of the insulationand that end of the coil, the top, Fig. 1, so 7 that the conductingportions of the coil are separated and insulated from this end of thecoil. The last turn of this layer and the first'of the next, e'tc.,terminate at the same distance from the opposite end of the coil,-

thereby providing. the coil with insulated ends, thus protecting andinsulating the bare windings inclosed between the insulating sheets 9.The strands of wire'. and the intervening strands of silk are Woundaroundthe core or shell'until one layer hasbeen provided, when a layerof insulating material,

a such as that described, is wound around it the winding is entirelyinclosed or covered by the insulation thus provided. A plural-- with itssides or'endportions extending to the ends of the shell 10.' By thisconstructlon the conducting portion of this layer of ity of layers arethen wound in like manner until the desired number have been provided,each layer being insiflated from those 4 adjacent thereto, and at coilby the sheets 9.

By using uninsulated or hare wire, as dethe ends or the .sci'ihed, thelength of the wire employed in tld making a coil of desired size,for-instance that usually provided for spark. plugs, may

he made much greater than the lengthhitherto employed, this beingapparent from the tact that the diameter of the hare wire is much lessthan insulated wire. This controdes. Fig. 2, wherein the last turn ofthe outer meal in struction therefore permits a greater number of layersof such wire to be used in making a coil of given size or diameter,thereby providing a spark plug coil that, under the usual Workingconditions, is of greater capacity or higher potential than thoseprovided with insulated wire.

As hitherto constructed, induction coils that are provided with windingsof bare wire have their bare terminals carried outto the opposite endsof the coil and being thus widely separated, no insulation is required.In devices of this type, however, where-it is desirable or necessary'tobring the terminals near together, the necessity for providing eflicientinsulation is a matter of considerable importance, more especially wherethey are carried outto one and the sameend of the coil and alsowhere-the construction of the plug necessitates arranging little spaceto receive them. The same necessity for providing an eflicientinsulation is apparent when the terminals are carried out at oppositeends and one is lead back, either within or withoutthe casing, toconnect it to one of the sparking electrodes, which are necessarily inclose relation, for without such insulation sparking and short circuit--ing would take place either between the terr the terminals neartogether, or PIOVldGS minals, as they are brought near together, or

between the terminal leading from the far' end of the coil and theadjacent portions of the coil, thewcasing, or other parts of the 10o luI P 1% providing spark plugs or analogous devices with coils having barewindings, therefore, the insulation of the terminals, especially whenthey are carried out to the same end of the coil should be veryeflicient or high to prevent sparking or grounding.

By employing'suitable envelops of insulating material such, for example,as the tabs or strips herein described, for inclosing the exposed endsof the terminals and by also carrying said. e'nvelops'into the body ofthe coil,'I provide eificient means for efiectually insulating theseterminals, so that sparking other than that produced at the sparkingelectrode-is eliminated.

While, obviously, one of the terminals of the secondary may if'desiredbe grounded upon the casing of the plug, inthe present instance,Ipreferably carry both terminals ll, 12, Fig; 2, of the secondary out toone and the same end of the coil forconvenience in connecting them tothe sparking elec- This arrangement is best shown in secondary winding,shownat. 15 in' the lower left hand corner of said figure, has itsterminal carried through an aperture 16 inthe folded end 17 of theinsulating strip 14. This strip is also arranged longitudinally upon thecoil in a manner similar to that in which the strip 13 is arranged.These folded strips respectively receive the terminals of the secondary,Fig. 2, between their folded portions, said terminals being centrallyand longitudinally arranged to extend between the inner surfaces of saidportions so that the terminals are completely embedded in insulatingmaterial, which insulates them from all conducting portions of the coilor plug. Said strips, 13, 1a, may be made of any suitable insulatingmaterial though, in the present instance, I prefer to employ a flexiblefabric, such as linen or silk, which is covered with varnish or oil ofhigh insulating properties and which causes the inner faces of thestrips to adhere, so that the metal terminals are longitudinally securedin position between the folds of said strips. By this construction, thepossibility of sparking between the several strands or layers of eithercoil and the terminals is prevented, since the latter are completely in-.closed in insulating material. The ends of these strips, shown at theright Fig. 2, and at the bottom of the coil, Fig. 1, are carried outbeyond the insulating ends of the coil to insulate the exposed ends ofsaid terminals from all conducting portions at that end of the coil, aswill be more fully described. Any suitable means may be employed tosecure the inner ends of the insulating strips 13, 14:, in position uponthe coil, one method being shown in Fig. 2, wherein the strip 1A isshown as secured to the last layer of the secondary by strips 18 ofsuitable. material, such as gummed or adhesive paper. The coil nextreceives a final layer of the insulating material, shown at 19, Fig. 2,preferably composed of the same varnished fabric. Finally, the coil isimmersed in a vessel containing an insulating, heat resisting,waterproof varnish or other similar medium. and preferably sterlingvarnish, which is allowed to soak in until the interstices or spacesbetween the different convolutions of the windings and the layers ofinsulating material, and especially between the ends of said insulatinglavers at the ends of the coil, have been filled with said varnish ormedium. The coil is then taken out and baked or otherwise dried afterwhich this process is repeated one or more times, finally leaving allconducting portions of the coil thoroughly coated and insulated by saidmedium and the separate parts of the coil pnited into one substantiallysolid strucure.

As thus prepared, the coil is inserted in a relatively thick removableshell or sleeve 20 .of waterproof, heat resisting, and insulatingmaterial, herein mica, which together with said coil is inserted intothe tubular metallic casing 5 .of the plug and which is preferably ofnon-magnetic material.

As here shown, the rear end of this casing 5 is closed by insulatingdisks or washers 21, 22, and 23, also of mica or like material, whichare held in position between the end of the coil and the inturned end,Fig. 1, of the casing. Immediately above this'end of the casing is ablock, here shown as a disk 24 of insulating material, for example,mica, which is provided with suitable apertures alined with and toreceive the primary terminals 4:. This disk is provided with bindingposts, 6, adapted to receive both the primary terminals and theterminals of an electric circuit (not shown) containing a battery,dynamo, or other suitable source of electromotive force and suitablevibration or other interrupting means. These posts and the block ofinsulating material are held in place upon the head of the casing 5 byany suitable means, here shown as screws 25, the heads, 26, of which arenotched to receive said terminals and are retained in the insulatingdisk 21.

As here shown, Fig. 1, the binding posts are apertured to receive theprimary terminals 4, which are maintained in firm conducting contacttherewith by means of removable plugs or wedges 4*, which are driven infrom the outside and act to close up the apertures and thereby entirelyclose this end of the plug and prevent the entrance of moisture. At itsfront end the casing is closed by a cap or head 27, Fig. 1, preferablyof metal having a threaded, reduced portion forming a nipple 28, adaptedto be screwed into the aperture provided in a wall of the enginecylinder. This casing head rests against an annular mica ring 29, inturn resting against a thick plate 30 of insulating material, hereinporcelain, which with said mica constitute a suitable heat resistingmedium between the end of the casing and said coil. This plate isprovided with a hub like or depending projecting central portion 31,fitting into a corresponding recess 32 in the adjacent face of the head27. The depending central portion of this head is provided withlongitudinally tapered passages to receive tapered hollow shells orconical sleeves 33, of insulating material, preferably of mica whichproject beyond the threaded end of the nipple 28, and at their innerends enter suitable recesses 34, centrally located in the dependingprojecting portion, 31, of said porcelain plate. To hold these sleevesfirmly in place within said head, I provide tapered plugs 35, 35, ofsuitable conducting material, for example, brass and drive them into theopen ends of the mica sleeves as shown in Fig. 1. Secured at and withinthe outer ends of these metallic plugs are the sparking electrodes 36,37, of suitable conducting material preferably German silver orplatinum, the electrodes 36 having a right angular arm 36 and theelectrode 3 consisting of a substantially' straight piece of wire. Theseplugs are driven into said sleeves to such depth that their lower ends,see Fig. l, are above the adjacent ends of the sleeves, the sparkingterminals being surrounded by the heat resisting and insulating walls ofsaid sleeves for. substantially their entire length, leaving only theirsparking points exposed. By this construction the metallic sparkingelectrodes are nearly inclosed by a shell of insulating material, allthe metal parts of the plug being widely separated therefrom; moreover'by arranging the sleeves so that their lower ends extend below saidmetal parts and driving the, conducting plugs in beyond said ends, thepossibility of a bridge of carbon deposit being formed between saidelectrodes or either or both of them or their plugs and the metallicportions of the nipple is eliminated. Moreoverthe oil'that enters orcollects in the open ends of the heat resisting mica sleeves ismaintained in a liquid state since said sleeves prevent the j conductionof enough heat from the ex- 1 I opening in the mica sleeve 33, to acentral longitudinal aperture in the plug 35.where it is secured bymeans of a taper wedge 88 plosion chamber to, their interior thus.preventing the carbonization of the oil therein.

The porcelain plate, best shown in Fig. 6, is centrally provided with'anaperture in approximate alinement with the central lead wire orsecondary terminalll, which is led through said aperture, said recess 34and the driven in from the outer end of the-plug.

Toprovide for suitably insulating the other secondary terminal 12, theporcelain disk 15 provided witha laterally extending and angular rib 39,Fig. 6, suitably aper-g tured as at to'receive said terminal 12' Thisaperturefleads inward to the recess 34, which communicates with theopening in l the tapered mica sleeve The secondary terminal 12 is ledthrough this aperture and said'mica sleeve and at its outer end issimilarly secured within the'metal plug 35 by a tapered" plug 38*, whichmaintains .the ter- "minalin electrical. contact with the conductingplug 35 and its. sparking terminal 37.

By this arrangement, the plugs within said mica sleeves effectually sealup all openings and close the plug against the entrance. of

moisture or gases.

An importantfeature of .lates to the thorough and efficient insulationof the secondaryterminals both from the conducting portions of thecasing and the adjacent conducting portions of the coils or their core.As here shown, referringto Fig. 2, the tabs or folded strips ofinsulatin material 13 and. 14, which extend lengthwlse of. and upon theinner and outer surfaces of the secondaries 11, 1.2 are carried out toand extend beyond the lower end of the coil (the right ig. 2) saidstrips being thick enough my invention reto prevent ruptureby sparkingfrom such adjacent conducting portions of the coil as are of higher ordifferent potential and wide enough to prevent the sparks passingbetween the secondary engaging faces of the folds of said strips. I

Referring now toFig. 1, the fold 13 of the insulating strip at the innerside of the terminal 18 is folded radially inward across difierentpotential and between which a spark might pass, unless properlyinsulated. As has been stated, the width of the strips is suflicient toprevent sparking laterally or between or across the strips and forms anefficient insulation at the end of the coil. The outer fold 14 of thestrip 14 extends downward and is arranged between the circumferentialedge of the porcelain plate 30 and the insulating sleeve 20 of thecasing thereby increasing the eiiiciency of the insulation atthat point..Similarly the outer fold 13 of the opposite strip 13 extends out wardradially between the coiled ends of the insulation layer of thesecondary and the upper or inner face of the porcelain disk and intosubstantial contact with the insulating sleeve 20. As here shown, theporcelain plate flattens the ends of the strips out across the adjacentface of the coil, so that the'recess formed between the inner face ofthe insulating and heat resisting porcelain plate and the adjacentinsulatedends of the coil of the secondary is partially filled with a.medium of high insulating properties which also forms a backing tosecure the coil in place within thecasing and prevent vibratory movementthereof. If desired, a

suitable waterproof, heat resisting and insulating cement, powder, orother like material, for example, a composition of rotten stone andshellac, .the latter dissolved in alcohol, or varnish and granulatedasbestos or mica may also be used to fill orpartially fill this recessand that at the top of the coil, to prevent displacement of the movableparts. This material, represented at' 41, not only perfects theinsulation of the coil but also prevents the admission of moisture andthe transmission of heat, which'is particularly desirable when the coilis mounted upon parts of relatively high temperature as in the presentinstance. *l'le the space between the insulated ends of the coil and theporcelain or mica plates may obviously be left vacant, the air thereinbeing a good non-conductor of heat, if a filler is used, it should becomposed of heat resisting and non-conducting material. It will beunderstood by those familiar with the art that spark plugs are subjectedto heat of'relatively high temperature and in constructing a coil plugit is exceedingly advantageous to provide it with every possiblepractical feature that tends to prevent heating it, that does nototherwise impair its efliciency. To this end, the casing, the closuresfor its ends, the lining shells, the coil, in fact, the entireconstruction of the plug includes novel features for maintaining theplug at asubstantially uniform temperature,

so that the coil may not be heated and its efiiciency and durabilitymaintained.

The inner face of the rib 39, referred to, extends inwardly at an anglefrom the center of said plate, as best shown in Fig. 6.

Iii-the positionin which said porcelain plate is secured within thecasing, Fig. 1, said rib indents the adjacent end portions 13, 14,

of said strips 13, 14, into the adjacent ends of the insulation layers 9of the secondary thereby increasing the insulation at that sisting andwaterproof, the sparking electrodes being mounted upon the samestructure with the secondary coil and directly connected therewith bymeans of heavily insulated leads, thus avoiding loss by grounding of thesecondary or lengthy secondary lead wires. Furthermore, the thickporcelain plate at the lower end of the plug, provides efficient heatresisting means which,

being interposed between the sparking ter minals and the induction coil,prevent injury to the latter by the action of heat.

As will be understood by those skilled in the art, the plug and itscontained coil described are adapted to be used with an exteriorlyarranged and independent vibrator magnet. The construction'andarrangement of the plug described permits the application of a number ofsuch plugs to the several cylinders of a multiple-cylinder engine whileusing a single exterior vibrator and vibrator magnet, the primary coilsbeing connected in multiple with eachother and in series with a maincircuit containing the vibrator-magnet and source of electrical energy.

This arrangement maintains the induction coils in close proximity to thesparking terminals thereby avoiding the use of exposed secondaryterminals or lead wires and securing the practical advantage of a singlevibrator for the several coils. The compactness of the plug permits itsaddition to the engine cylinder, while occupying practically the samespace or room as the ordinary spark plug.

So far as I am aware, this is the first instance in the art in whichcoils composed of windings of bare wire, or coils provide-l with'heavilyinsulated terminals have been provided for use in spark plugs, therebyeliminating the use of exposed secondary lead wires and auxiliarysparking devices.

One feature of my invention to which especial attention may be directedand which may be embodied in other specific coil con.- structions thanthat herein disclosed, is the complete insulation which is afforded thesecondary lead in passing from the coil to the sparking electrode bymeans of the continuous overlapping insulating elements which arecompactly but efiiciently arranged between the end of the coil and theelectrode., 1

While in the embodiment of my invention herein disclosed, the secondaryterminals of the spark coil are insulated from one another and thecasing and both directly connected to the sparking electrodes, myinvention is not limited to such specific arrangement and it is to beunderstood that I contemplate applying the broad features thereof tospark plugs in which one of the terminals may be indirectly connected toone of the sparking electrodes as by grounding it upon the casing,though I prefer the present construction which is much more efficient.

While in the particular embodiment of my invention herein selected forillustrative purposes only, I have described the same with reference toa spark plug and to a coil having windings of particular type andprovided'withinsulating strips of fabric, it is to be understood that myinvention is not limited thereto nor to the specific details ofconstruction and arrangement, 1 since the same is capable ofmodification within wide limits without departing from the spirit andscope of my invention.

1. In a device of the type described, a spark coil having a terminalcarried out to extend from one end thereof, means comprising fiat stripsofinsulating material laidlengthwise upon and enveloping said terminalfor inclosing and insulating the exposed end thereof from the adjacentconducting portions of said coil, and a pair of sparking electrodes withone of which said terminal is connected.

2. In a device of the type described, a

spark coil having a terminal carried out and extending from one endthereof, flat strips of insulating material laid lengthwise upon andenveloping said terminal and also extending into the coil to cover andinsulate said terminal from the adjacent conducting portions of said,coil, and a pair of sparking electrodes with one of which said termimlis connected.-

In a device of l the type described, a

spark coil having terminals carried out and extending from one'endthereof envelops of insulating material inclosing each of said adaptedto-conform to the circumference of the coil without substantiallyincreasing the diameter thereof and longitudinally arranged upon saidterminal for covering and insulating it from the conducting portions ofsaid coil, and a pair of sparking electrodes to one of which saidterminal is coni nected.

5. A spark plug coil having sparking electrodes, a winding of bare wire,and wire terminals connected to said sparking elee-' trodes, insulatingmeans between adjacent convolutions of said wire, layers of insulatingmaterial between adjacent layers of said wire, a layer of. insulatingmaterial about the outer layer of said wire, insulating -mean s forprotecting said wire terminals,

the last-mentioned insulating means being distinct: from and extendingbetween two adjacent layers of said insulating material, and othercooperating, insulating means leading to the sparking electrodes.

'6. A spark plug comprising a casing, a sparking electrode, an inductioncoil within sald casing provided with 'a winding of bare wire and a Wireterminal, insulating means for protecting the body of the .coil toinsulate the same from the bare windings thereof, and separate anddistinct insulating means covering said wire terminal and lead:

ing from. the sparking electrode and terminating at a point within thefirst-mentioned insulating means;

' '7. In a spark plug the combination of a casing, an induction coilwithin'sa'id casing provided with a winding of bare wire and a wiretermnal, means for nsulat ng the convolutionsof'sa'id coil from one another,in-

' sulating means for. protecting the otherwise I v i eais bare andexposed end of said terminal and also extending into the body of thecoil and terminating within the insulation of the bodyv of the coil toinsulate the wire terminal from the bared metallic windings of the coil,a filler of insulating material for sealing the end of said casingadjacent said terminal, and a pair of sparking electrodes with one ofwhich said terminal is connected.

8. A spark plug having a casing, a coil within said casing havingprimary and secondary windings, the latter being wound with bare wire,means for insulating the convolutions of said wire from one another,means whereby the casing may be attached to an engine cylinder,a-sparking electrode, a

bare wire secondary terminal leading from the I attaching'end of thecasing and connected 'with said electrode, and continuously arranged butindividually distinct insulating elements extending from said electrodeto and terminating within and-"overfllaidby the insulation of thebody ofthefcdil for insulating said otherwise bare t fmil lal.

9. A spark plug having a casing, a coil to provide a continuousinsulation for the a I terminals.

ing a head adapted to be secured to an engine cylinder, sparkingelectrodes carried by said head, van induction coil within said 10. Aspark plug comprising a casing havcasing having windings of bare wirewith means for insulating the adjacent convolutions from one another, awire terminal carried out'to the end of the coil adjacent said head -andconnected to one of said electrodes,

and an envelop of insulating material dis v tinct from said convolutionsinsulating means for inclosingand insulating the portion ofthe otherwlsebareiwire terminal int-rmediate said coil and said head, said envelopextending within and being inclosed and overlaid by the insulating meansof the body of the coils 11. A spark plug comprising a casing having ahead adapted to besecured to an engine cylinder,"sparking electrodescarried by said head, an induction coil wi thin said casing havingwindings of bare wire with means for in'sulatin the adjacentconvolutions from one anot er and a wire terminal carried out to the endof the coil adjacent said head and connected to one of said electrodes,an envelop of insulating material distinct from said convolutionsinsulating means, and inclosing and insulating the portion of theotherwise bare wire terminal intermediate said coil and said head, saidenvelop extending within and being inclosed and overlaid by theinsulating means of the body of the coil and a filler of insulatingmaterial for insulating the end of the coil adjacent said head.

12. A sparking plug provided with a casing having a head provided withmeans for attaching it to an engine cylinder, an induction coil woundwith bare wire within said casing having one of its bare wire terminalscarried out to the end of said casing adjacent said head, means forinsulating the convolutions of said wire from one another, a plate ordisk of insulating material between said head and the adjacent end ofthe coil, and provided with means to receive said terminal, and anenvelop of insulating material distinct from said convolutionsinsulating means for inclosing and insulating the portion of saidterminal between said plate and the adjacent end ofthe coil, saidenvelop extending within and being inclosed and overlaid by the.insulating means of the body of the coil.

13. A sparking plug provided with a casing having a head provided withmeans for attaching it to an engine cylinder, an induction coil withinsaid casing having one of its terminals carried out to the end of saidcasing adjacent said head, a plate or disk of insulating materialbetween said head and the adjacent end of the coil, and provided withmeans to receive said terminal, an envelop of insulating material forinclosing and insulating a portion of said terminal between said plateand the adjacent end of the coil and a heat resisting filler for fillingthe space between said plate and said coil and enveloping said terminal.

, 14. A spark plug having a casing, an induction coil within said casinghaving its terminals carried out to one end of the coil, an insulatingplate at the terminal end of said coil and provide with recesses, shellsof insulating material arranged in said recesses to receive saidterminals, and envelops of insulating material for insulating theexposed portion thereof and the adjacent conducting portions of saidcoil, each of the envelops having end portions extending laterallybetween the end of said coil and the adjacent face of said plate.

15. In a device of the type described, an induction coil havingterminals carried out and extending from one end thereof and envelops ofinsulating material for each of said terminals for insulating theexposed ends thereof, an inner portion of each of said envelopsextending across. the end of the coil and providing a double layer ofinsulating material between vsaid terminals and the conducting portionsof said coil, a casing in which said coil is mounted, a plate ofinsulating material for closing said casing at the terminal end of saidcoil and provided with means to receive said terminals, said plate beingarranged to press the ends of said envelops against the adjacent end ofthe coil and supporting the latter within said casing, and sparkingelectrodes with which said terminals are connected.

16. A sparking plug for internal combustion engines comprising a casing,an induction coil arranged therein having primary and secondary windingsand a secondary terminal carried out to one end of said casing, a platefor closing the end of the casing adjacent said terminal and providedwith means to receive said terminal, a head exterior to said plate andsecured to said casing and provided With means to adapt the same to beattached to an explosion engine, an envelop of insulating material forsaid terminal, means for insulating the exposed portion of said terminalbetween the end of the coil and the inner face of said plate and toprevent sparking between said terminal and the adjacent conductingelements of said coil or said plug, an insulating shell carried by saidhead, a metallic conducting plug carried thereby, means for securingsaid terminal thereto, and a sparking electrode carried by saidconducting plug.

17. A spark plug comprising a casing, a coil therein provided with aplurality of convolutions of bare wire, intervening convolutions ofinsulating material and an outer layer of insulating material, and aterminal also of wire provided with an insulating envelop distinct fromsaid material to prevent sparking between said terminal and the adjacentwire conducting portions of said coil or said casing, said envelopcommencing within the body of the coil intermediate said outer layer andthe adjacent layer of the wire and extending beyond the end of the coilto insulate said terminal from the adjacent conducting portions at theend of said coil, and sparking electrodes to one of which said terminalis connected.

18. A spark plug provided with a casing, ahead therefor, a coil withinsaid casing, an

insulating shell mounted on and projecting outwardly beyond said head,and a sparking electrode having its inner end secured at a point withinand inwardly beyond the outer end of said shell, the latterprojecting-from said head and enveloping said electrode beyond the pointwhere it is secured to a point adjacent the sparking terminal thereof.

19. A spark plug having a casing, an induction coil therein, the latterprovided with a secondary wound with bare wire, and wire terminals, asparking electrode to which one of said terminal electrodes isconnected, an insulating body at the terminal end of said secondarywinding, through which-insulating body the said secondary terminal.passes, and an insulating envelop inclosing an otherwise bare wireterminal and extending into and terminating Within the body of the coiland filling a portion of the'space between the said body and the coil. h

, 20. A spark plug having an induction I coi1,-an insulating plate atone end thereof, insulating material between said plate and said coil, aterminal passing from said coil two subscribing Witnesses.

ISRAEL 0. oRsWELL Witnesses:

ROBERT H. KAMMLER, SIDNEY F. SMITH.

